Microphone with fuse



17, 1950 o. D. M. GUTHE ET AL MICROPHONE WITH FUSE Filed Sept. 1., 194

FIG.

/N[/E/V TOPS WYM 4 A TTORNEV Patented Jan. 17, 1950 010i 1'). M. Guthe, Scarsdale, N. Y., and OscanA. Shann, Short Hills, N. :;;J.,.,,assignors to Bell- Telephone Laboratories, lncorporated,

New

York, N. Y., a corporation of New York Application September 1, ima serial No. 61 3,9184

This invention relates to telephone transmitters and particularly to improvement in such transmitters to protectfthem against overloading. V LI-Ieretofo're arrangements have been provided in connection with'electrical circuits and associated telephone apparatus for protection against abnormally high voltages caused by overloading or acoustic shocks. One method was to incorporate shunting devices for such abnormal voltages as for example by inserting across a circuit an element having a negative temperature coefilcient of resistance so that when such high voltages occurred in the circuit, they were by-passed by the circuits around the apparatus which they were designed to protect.

It is a feature of the present invention to provide a transmitter structure in which such protective elements are incorporated as permanent parts of the transmitter. The invention may be incorporated in the carbon button of a standard transmitter and may in this case take the form of a ring of a material having a negative temperature coefdcient of resistance in which a metal diaphragm, in place of the usual mica diaphragm, is embedded. In the case of overloading or abnormal voltages in the line to which the transmitter is connected, this element will increase in temperature and thus quickly reduce its resistance and thereby protect the carbon granules from pitting by the momentary shunting of these excessive currents. Another form of this invention may be the substitution of such an element in place of a ceramic insulation element embedded in the transmitter where such an element forms part of the carbon chamber.

This invention has been illustrated in the ac companying drawings in which:

Fig. 1 shows a standard carbon button in which the applicants invention has been incorporated;

Figs. 2 and 3 show modifications of the applicants invention as applied in the button shown in Fig. 1; and

Fig. 4 shows a special type of transmitter in which the applicants invention has been incorporated.

Referring now to the drawings, Fig. 1 shows a standard transmitter button comprising a casing I having a cavity. and an electrode, consisting of the usual metal disc 2 and carbon disc 3, inserted in the bottom of this cavity. The opposing electrode comprises a metal disc 4 and a carbon disc 5 and the space between the electrodes contains the usual carbon granules 6. To the metal disc 4 is applied a metal diaphragm I by means of a nut 8. This metal diaphragm has its outer rim embedded 1 Claim. (01. 179-122) in the elementll ,This element is of the type having a negative temperature coefficient of resistance and isclamped over the cavity by means of a cap ll screwed on casing l. The disc 4 is secured to the usual diaphragm l2, The inside cylindrical surface of the cavity is insulated by a member l3. To the casing I is secured one terminating end I4 of the usual transmitter circuit while the other terminating end l5 of this circuit is secured in the usual manner to the diaphragm for the passage of the talking current between the two electrodes for the operation of diaphragm l2 in accordance with voice current variations.

In the case of overloading of the circuits l4 and I5 by abnormal voltages, this element It! would quickly increase its temperature and thus reduce its resistance and thereby permit these voltages to be shunted around the carbon discs and granules and thus protect them from pitting or other injuries. That is, this element may be so designed and possess such properties that for low voltages within the voice current level only a minute fraction of the current will be diverted thereby, whereas when abnormally high voltages occur much greater percentages of current will flow through this element to protect the carbon granules. Typical of suitable materials for the element 10 are those disclosed in Patents 2,258,646 granted October 14, 1941, to R0. Grisdale and 2,282,944 granted May 12, 1942, to E. F. Dearborn and G. L. Pearson.

In Fig. 2 the element I0 is shown as encased for protection against injury and to facilitate handling by a metal housing ll of a U-shaped cross-section. In Fig. 3 this element In is shown in the form of a ring on the underside of the diaphragm I and these two elements insulated from the cap I l by means of an insulation ring 20.

In Fig. 4 a different type of transmitter is shown, in which the casing 22 is provided with an opening 23 closed at one end by means of a flexible, non-metallic disc 24 stifiened by a metal spider member 25. These members 24 and 25 are then secured between the usual diaphragm 26 and a cup-shaped electrode 21 extending down into the opening in the casing 22. This opening is filled with carbon granules 30 and closed at the opposite end by an opposing electrode 32 having a contact ring 33. This latter electrode is secured to the casing 22 by means of an insulation disc 34 having on its outer side a metallic ring 35 clamped down over the casing by means of the screw cap 36. The electrode 32 rests for this purpose against an element in the form of a ring inserted in the opening and numbered 38. This material. 539. z This transmitter iSn otherwiseidenticalwith'the construction disclosed in the Patent 2,042,832 to A. F. Bennett et al., of June 2, 1936. Circuit connections are made between the electrodes by a conductor 40 connected. to ring 33 and a conductor 4| connected to cap 36.' In 7 this type of transmitter when subjected to overloading or abnormal voltages on the conductors 40 and 4|, element 38 will quicklyvchange its" temperature and thus reduce its resistance and" thereby shunt the excessive 'yoltagesraround the:

carbon granules from the electrode 33 to the casing 22 to protect these granules against-injury.

What is claimed is: 7 A-telephone transmitter comprising ;-pairof line terminals, a-casi-ng having anopening therein; a ring element'in said opening, said ring element-having a negative coefiicient of'resistance,

a-first electrode adjacent said ring element insaid opening and electrically connected to one side of said ring element and to one of said terminals, a second electrode in said opening -electrically connected to another side of said ring element and to the other of said terminals, comminuted resistance material between said electrodes, diaphragm means for'yibrating said second electrode, and insulating meansbetween said ring element and said resistance material.

OLOF D. M. GUTHE.

OSCAR A. SHANN.

REFERENCES CITED .Thei followingreferences are of record in the fil'e of this patent:

. UNITED, STATES PATENTS Number Name Date 1,159,205 Frank NOV. 2, 1915 1,415,748 Weintraub May 9, 1922 2';0'42,822 Bennett June 2, 1936 2,237,448 Reinhard Apr.v 8, 1941 22581646 Grisdale Oct. 14, 1941 2,287,998 Johnson June 30, 1942 

